This invention relates to a method and an apparatus for continuous drainage of a curd for stringy cheese, particularly Mozzarella.
Among the stringy cheeses, Mozzarella which is a fresh cheese, is hermetically packed in bags in the form of balls immersed in a liquid. Its body is white and fibrous, but spongy in structure, and its taste is delicate, mild and slightly salted.
Traditionally, Mozzarella is made by standardizing the fats content of the milk, pasteurizing the milk, adding lactic cultures based on Streptococcus thermophilus, coagulating the milk with rennet and cutting the curd into grains the size of a hazelnut or a nut. The critical drainage phase of the process is then carried out to give the curd a suitable dry extract degree and a suitable stringing point through the actions of the operators and the lactic fermentation process. The stringing point is the degree of demineralization of the curd which enables the maximum plasticity of the body to be obtained by heating. It is during the drainage phase that the curd recombines to give a "pre-cheese".
The drainage phase has to be carried out slowly with great care. It is carried out in batches in gutters placed on trolleys which involves considerable manual work and takes up considerable floor space. After drainage, the pre-cheese is in the form of loaves which are cut into blocks ready for stringing.
Stringing comprises treating a block of pre-cheese obtained after drainage, which has a clearly defined pH and dry extract degree and which is cut into pieces in hot water, in a kneading trough to obtain a spongy and elastic mass which can easily be dosed, shaped into balls, hardened by immersion in cold water and, finally, packed in bags.
In contrast to the traditional European method, production on an industrial scale carried out mainly in the United States comprises acidification with citric acid which has the advantage, providing the acidification parameters are carefully controlled, of virtually eliminating the need for drainage so that the curd as a whole can be directly subjected to stringing. However, the characteristics of the end product, particularly its pH value of approximately 6, its whitish colour, its insipid taste and its poor keeping properties, which require a distribution circuit cooled to 4.degree.-6.degree. C., distinguish it from the traditional European product which has a pH of 5.1 to 5.2, a slightly yellowish colour, an aromatic taste of fermented milk and good keeping properties cooled to around 8.degree.-10.degree. C.
Although the phases of coagulation and stringing can be carried out continuously, i.e., can be mechanized without difficulty, the same has not hitherto been the case with the drainage phase that is necessary when the technique involves biological acidification, that is to say, solely biological or mixed acidification, i.e., partly with citric acid or lactic acid and partly by the action of lactic ferments.
A process and apparatus for the continuous drainage of curd intended for the production of Cheddar are described in U.S. Pat. No. 4,309,941. The apparatus in question enables a drained curd to be continuously produced under controlled conditions involving movement between fixed vertical walls by means of a system of several conveyors surrounded by an enclosure on which the layer of curd is successively deposited. Close study of this apparatus has shown that it is not suitable for the production of Mozzarella. The formation of a single, more or less thick curd layer, which is subjected to irregular mechanical stresses during its travel under the effect of the traction forces, results in the formation of a skin covering the pre-cheese which prevents progressive drainage and homogeneous demineralization of the pre-cheese leading to a curd drained at the desired pH. In addition, the deposition and transfer of the curd layer are not regular. These conditions are not suitable for stringing.